The OP has been asking whether it's reasonable for Amex to shut down his accounts and keep the annual fees. He has said the reason for the shutdown is not relevant, but I think that it is. If the behavior causing the shutdown is egregious enough, then Amex's response can be considered justified. No one can answer without knowing what he did.
He claims that Amex hasn't told him the reason, and he doesn't know what it is. This seems suspicious to me. If it was something so bad that Amex shut down everything, you most likely know what it is. If he got shut down because he was an AU of someone who did something bad, he most likely knows what that is as well.
I am leaning toward the upgrade offers rather than multiple cards of the same type. Were the upgrade offers presented to him in his account, or did he find upgrade links posted somewhere?